Mpox is caused by the monkeypox virus, which is related to the smallpox virus and causes a similar, but usually milder, illness.
Mpox is caused by the monkeypox virus, which is related to the smallpox virus.
A rash is the most prominent symptom.
Diagnosis of mpox is usually made by taking a sample from a skin lesion and testing it for the virus's genetic material (DNA).
A vaccine to prevent mpox is available.
Treatment of mpox is mostly directed at relieving symptoms, and antiviral drugs may be helpful.
(See also Overview of Viral Infections.)
Monkeypox and smallpox are part of a group of viruses called orthopoxviruses. They are not related to chickenpox, which is caused by varicella-zoster virus and is part of another viral group.
Despite its name, the monkeypox virus does not come from monkeys. Although the reservoir (an animal that is the source of infection) is unknown, the most likely animal sources are small rodents (for example, squirrels) in the rain forests of Africa, mostly in western and central Africa. The disease caused by the monkeypox virus was also originally called "monkeypox," but in November 2022 the World Health Organization introduced the name “mpox” for the disease caused by the virus (see WHO recommends new name for monkeypox disease).
In 2022, mpox cases were reported in approximately 70 countries that do not usually have mpox infections, including several European countries and the United States. This is a new situation because previous sustained person-to-person transmission of mpox had been mainly in Africa. The World Health Organization (WHO) declared the 2022 mpox outbreak a public health emergency of international concern (see WHO: Monkeypox Outbreak 2022). The number of new cases in the United States has dramatically decreased since the peak in August 2022.
Medical organizations are investigating how people have been exposed and how the infection is being spread during the 2022 outbreak. Many cases have occurred in men who have sex with men, but it is unknown if this pattern will continue and if the infection is sexually transmitted.
Historically, mpox infection in people was found mainly in sporadic cases in Africa and occasional epidemics. Most cases have occurred in children in the Democratic Republic of the Congo.
Starting in the 2000s, the number of cases has been gradually increasing in Africa. Reasons may include the following:
People are no longer being vaccinated with the smallpox vaccine, which helped protect them from mpox.
People are moving into areas where the animals that carry the virus live.
Prior to 2022, cases outside of Africa were directly linked to travel to western and central Africa or animals imported from the region. In the United States, an outbreak of mpox occurred in 2003, when infected rodents were imported as pets from Africa. The rodents spread the virus to pet prairie dogs, which then infected people in the Midwest.
Mpox spreads in few ways (see also Centers for Disease Control and Prevention (CDC): 2022 U.S. Mpox Outbreak). It can spread from person-to-person through
Direct contact with the infectious rash, scabs, or body fluids
Respiratory secretions during prolonged, face-to-face contact, or during intimate physical contact, such as kissing, cuddling, or sex
Touching items (such as clothing or linens) that previously touched the infectious rash or body fluids
The placenta, from pregnant people to their fetus
Mpox can spread when people come into contact with infected animals, probably through bites or scratches from an animal or through preparing and eating infected animal meat.
Symptoms of Mpox
Mpox causes symptoms that are similar to those of smallpox. As in smallpox, the mpox rash begins as flat, red spots. The spots then turn into blisters, which fill with pus (forming pustules). After several days, the pustules crust over. Prior to the 2022 outbreak, the rash would often begin on the face and spread to other parts of the body, including the palms and soles. During the 2022 global outbreak, however, the rash often starts on or near the genitals or in the mouth, is often painful, and may not spread or progress through the typical stages.
Symptoms may also include fever, chills, headache, muscle aches, backache, extreme fatigue, and prominent swollen lymph nodes. These symptoms may occur before, during, or after the rash appears.
Mpox can make people more likely to develop other infections. Some people with mpox develop bacterial infections in the skin and lungs.
The illness is usually milder than smallpox, but it can cause death. No deaths occurred during the 2003 outbreak in the United States. In the 2022 outbreak, there have been a few deaths among thousands of cases.
Symptoms may start 1 to 2 weeks after a person gets infected, but it can take as long as 3 weeks for symptoms to appear. People are infectious (meaning they can spread the virus to someone else) from the time symptoms start until all lesions have crusted and scabs have fallen off to reveal healthy skin. This typically takes 2 to 4 weeks.
Image courtesy of the Public Health Image Library of the Centers for Disease Control and Prevention.
Image from U.K. Health Security Agency.
Image from U.K. Health Security Agency.
Image from U.K. Health Security Agency.
Image from U.K. Health Security Agency.
Image from NHS England High Consequence Infectious Disease Network.
Image from NHS England High Consequence Infectious Disease Network.
RICHARD USATINE MD / SCIENCE PHOTO LIBRARY
Image courtesy of the Public Health Image Library of the Centers for Disease Control and Prevention.
Image from U.K. Health Security Agency.
Image from U.K. Health Security Agency.
Image from U.K. Health Security Agency.
Image from U.K. Health Security Agency.
Image from NHS England High Consequence Infectious Disease Network.
Image from NHS England High Consequence Infectious Disease Network.
RICHARD USATINE MD / SCIENCE PHOTO LIBRARY
Diagnosis of Mpox
Doctors consider mpox as a possible cause of symptoms in anyone who presents with a rash that looks like typical mpox skin lesions.
Diagnosis of mpox is usually made by taking a sample from a skin lesion and testing it for the virus's genetic material (DNA).
Other tests people may have to detect monkey pox may involve sending samples of infected tissue to a laboratory for the virus to be grown (cultured) and analyzed; blood tests for antibodies to the monkeypox virus; and examining a sample of infected tissue under a microscope.
Treatment of Mpox
Prevention of Mpox
Two vaccines used for prevention of smallpox may be used for the prevention of mpox: JYNNEOS and ACAM2000 (see CDC: Mpox Vaccination Basics). Past data from Africa suggest that the smallpox vaccine is at least 85% effective in preventing mpox, because monkeypox virus is closely related to the virus that causes smallpox. A smallpox vaccine may be offered to people at high risk of exposure to mpox in areas where there are local outbreaks and to healthcare providers in contact with infected people.
The JYNNEOS vaccine is a live but weakened vaccinia virus that does not reproduce in the person who receives it. JYNNEOS is the main vaccine used in the United States in the current outbreak. It is used for the prevention of mpox in adults 18 years of age and older who are at high risk of mpox or after a recent known or presumed exposure to mpox. JYNNEOS may also be given to people at high risk of social exposure to mpox in the setting of local outbreaks. People who have a weakened immune system may receive the JYNNEOS vaccine (unlike ACAM2000) but may have a diminished response.
The ACAM2000 vaccine contains live vaccinia virus, which is related to the smallpox virus and provides cross-immunity to the monkeypox and smallpox viruses. It is given to people who are at high risk of mpox (or smallpox). ACAM2000 is given by rapidly jabbing a small area 15 times with a specially designed needle that has been dipped in the vaccine. Vaccination with ACAM2000 is dangerous and not recommended for some people, especially those with the following risk factors:
Weakened immune system (such as those who have AIDS or who take medications that suppress the immune system)
Skin disorders (particularly atopic dermatitis [eczema])
Eye inflammation
Heart condition
Age under 1 year
Pregnancy
People with mpox who are not in the hospital should
Isolate at home until the lesions have resolved and scabs have fallen off and a fresh layer of intact skin has formed
Avoid direct physical contact with other people and animals
Not share potentially contaminated items, such as bed linens, towels, clothing, drinking glasses, or eating utensils, and should clean and disinfect commonly touched surfaces and items
Wear a mask if close contact with others in the home is necessary
For more detailed guidance about how to isolate safely at home after being diagnosed with mpox, see CDC: Mpox: Isolation and Infection Control: Home.
More Information
The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.
